About 4.5 billion years ago, the miscellaneous material orbiting a
star at the edge of the Milky Way coalesced into a planet that we call
Earth. It took another billion years—a thousand million years—before
it cooled enough for life’s self-replicating biochemical processes
would flourish in the primeval stew of the oceans. Another billion
years was required before multicellular organisms would evolve. Not
until about 500 million years ago did fungi and plants appear on the
land that had risen out of the oceans. Insects evolved in this
terrestrial ecology. Then 100 million years was required for some
marine animals to transition to the continents on their long and
convoluted journey from simplicity to complexity. Thus began the magic
of life and death that has alternated between the prolific and the
extinct throughout the subsequent eons of history. We, as a distinct
species, evolved as Homo sapiens only about 200,000 years ago.